The invention relates to a tool turret for a machine tool, in particular a lathe, comprising a turret head mounted on a turret head carrier for rotation about a turret axis and having a plurality of tool stations, the turret head being lockable against rotation and having at each of a plurality of its tool stations a receiving means for the insertion of a tool holder for a tool adapted to be rotatably driven, the tool holder having a tool spindle, also comprising a drive shaft defining a working position for the tool stations, the turret head being rotatable about the turret axis relative to the drive shaft, as well as a coupling having at least two coupling elements separable from one another for providing a rotary drive connection between the drive shaft and the tool spindle of a tool holder located in the tool station taking up the working position, wherein a first coupling element is arranged on the drive shaft and a second coupling element on the tool spindle.
The tool turrets in general use correspond to the type of construction defined above, and a tool turret of this type is disclosed, for example, in DE-A1-36 30 966 and U.S. Pat No. 4,704,926. This known tool turret is provided with a two-part, so-called HIRTH tooth system (curvic coupling), the one toothed ring of which is securely connected to the turret head carrier and the other toothed ring of which is securely connected to the turret head. In order to index the turret head, i.e. in order to be able to rotate it about the turret axis, the turret head is advanced in the direction of the turret axis and this causes the one toothed ring of the HIRTH tooth system to be lifted off the toothed ring fixed on the turret head carrier. A central shaft serving to drive the tool is rotatably mounted in the turret head carrier coaxially to the turret axis and it bears on its front end facing the turret head a first bevel wheel of a miter gear which is arranged in the interior of the turret head and comprises for each tool station of the turret head a driven shaft which is rotatably mounted in the turret head, is radially oriented in relation to the turret axis and provided with a second bevel wheel. When the turret head is unlocked, all the driven shafts are also displaced so that their bevel wheels are lifted off the bevel wheel of the central shaft. A complete, actuatable coupling is located between each driven shaft and each tool spindle. The turret head carrier has a projection associated with the tool station located in working position. Due to this projection and a piston mounted in the turret head for displacement in axial direction, that coupling which is associated with the tool station located in working position is engaged.
This known tool turret has a number of disadvantages which are typical for all the known tool turrets of the type mentioned at the outset: In order to unlock the turret head, this must be moved in axial direction before it can be rotated, i.e. indexed further, about the turret axis. In view of the relatively large mass of the turret head and all the tools carried by it, this axial movement can be carried out only at a moderate speed since considerable shocks otherwise occur, i.e. it is not possible to index the turret head quickly and relatively long idle times, in which work cannot be done with a tool of this tool turret, are the result. An additional disadvantage of the known tool turret described in the aforesaid is the fact that all the gear elements, which are arranged after the bevel wheel of the central shaft, and their bearings must also carry out the axial movement together with the tool turret. Furthermore, the couplings between the driven shafts of the miter gear and the tool spindles are of a relatively complicated construction and special actuating means are required for actuating these couplings since any indexing of the turret head presupposes an actuation of that coupling located in working position. These are circumstances which not only lead to higher production costs but also preclude any reduction in the indexing times for the turret head. Finally, the tool spindles of the tool stations not located in working position can rotate unintentionally and in an undesired manner, in particular during indexing of the turret head (some tools must be used at the correct angle of rotation).
The same applies for another known tool turret (DE-PS 37 30 561), the turret head of which must also carry out an axial movement in order to be unlocked. A drive shaft extending parallel to the turret axis is mounted in the turret head carrier of this known tool turret eccentrically to the turret axis. A first bevel wheel of a miter gear is attached to the end of the drive shaft facing the turret head. This bevel wheel engages with a second bevel wheel of the miter gear in the working position of the turret head and this second bevel wheel is attached to a driven shaft of the miter gear, which is rotatably mounted in the turret head and extends radially to the turret axis. When the turret head is unlocked, the bevel wheel of the miter-gear driven shaft also disengages from the bevel wheel of the miter-gear drive shaft. So that the miter-gear driven shaft and, with it, the tool drive spindle of the associated tool holder cannot rotate unintentionally, the miter-gear driven shaft has a recess at one point of its circumference, in which a spring-loaded locking bolt, which is guided for displacement in the turret head, engages when the turret head is in its indexing position. The locking bolt is lifted out of the recess in the miter-gear driven shaft by an axially oriented pin provided on the turret head carrier when the turret head is moved back into its working position. In this known tool turret, as well, all the tool stations which are provided to be equipped with a tool holder for a drivable tool are provided with a miter-gear driven shaft whereas only one single miter-gear drive shaft is provided, namely for driving the tool which is located in working position--the miter gear is not, therefore, formed by the same two bevel wheels all the time.
Finally, the same applies for another, known tool turret which results from DE-PS 39 29 803 and, with respect to the above comments on the tool turret according to DE-PS 37 30 561, differs from the latter only in that the tool spindles of the tool holders having drivable tools also form the miter-gear driven shafts and are inserted into or removed from the turret head with the actual tool holders.
The object underlying the invention was to provide a tool turret of the type mentioned at the outset which is improved over the state of the art in at least one of the following points: Shortening the indexing times of the turret head, simple (from the point of view of construction and/or procedure) coupling in and out of driven tools, and preferably in a defined angular position of the tool, creating the preconditions for the use of a miter gear of higher quality for driving the tool spindle or spindles so that, for example, permanently higher tool rotational speeds are possible.